Gas-filled electric discharge devices

ABSTRACT

A gas-filled device for use in T-R and T-B cells which is of coaxial form and simple construction. The device essentially comprises a conductor extending coaxially through a tubular gasfilled envelope, and capacitive and inductive elements which extend radially from the conductor and together form a resonant circuit. The two elements are suitably formed integrally and extend in opposite directions from the conductor.

United States Patent Inventor William Ives Moore Watford, England Appl. No. 853,464

Filed Aug. 27, 1969 Patented Mar. 2, 1971 Assignee The M-O Valve Company Limited London, England GAS-FILLED ELECTRIC DISCHARGE DEVICES 7 Claims, 2 Drawing Figs.

US. Cl 315/39, 333/13 Int. Cl.; l-l0lj 7/46, HOlp 1/04 Field ofSear-ch 315/39;

[56] References Cited UNITED STATES PATENTS 2,587,305 2/1952 Fiske 315/39 2,602,908 7/1952 Linder 315/39 2,978,609 4/1961 Duffy et al. 315/39 3,209,285 9/1965 Manwarren et al 333/13 Primary ExaminerEli Lieberman Assistant Examiner-Saxfield Chatmon, Jr. Attorney-Kirschstein, Kirschstein, Ottinger and Frank ABSTRACT: A gas-filled device for use in T-R and T-B cells which is of coaxial form and simple construction. The device essentially comprises a conductor extending coaxially through a tubular gas-filled envelope, and capacitive and inductive ele ments which extend radially from the conductor and together form a resonant circuit. The two elements are suitably formed integrally and extend in opposite directions from the conductor.

GAS-FILLED ELECTRIC DISCHARGE DEVICES This invention relates to gas-filled electric discharge devices.

The invention relates particularly to gas-filled electric discharge devices of the kind which present a short circuit to radio frequency energy above a predetermined power level due to ionization of the gas filling, but which are effectively transparent to radio frequency energy at lower power levels. One particular application of such devices is in T-R and T-B cells.

It is an object of the present invention to provide a gas-filled electric discharge device of the kind specified which is of coaxial form and is of simple construction.

According to the present invention there is provided a gasfilled electric discharge device of the kind specified comprising a sealed, gas-filled, tubular envelope of conducting material through which a conductor extends substantially coaxially, a first member of electrically conductive material which is electrically connected to the conductor and extends radially from the conductor to a position closely adjacent the inner surface of the envelope so as to form a capacitive element, and a second member of electrically conductive material which extends radially between the conductor and the envelope and is electrically connected to both, so as to fonn an inductive element, the capacitive and inductive elements forming a resonant circuit at a frequency at which the device is intended to operate.

The first and second members are suitably formed integrally with one another and may conveniently be arranged to extend in opposite directions from the conductor.

One arrangement in accordance with the invention will now be described by way of example with reference to the accompanying drawing in which:

FIG. 1 is a sectional view of a T-R cell; and

FIG. 2 isa cross-sectional view on the line II-II in FIG. 1.

Referring to the drawing, the cell includes a hollow cylindrical sealed envelope comprising a metal tube 1 into each end of which is sealed a centrally apertured disc 2 of dielectric insulating material. A metal rod 3 extends coaxially through the envelope, the rod 3 being of reduced diameter in the regions where it passes through the apertures in the discs 2 to provide substantially refiectionless transmission of radio frequency energy through the dielectric filled regions of the tube 1 at the frequencies at which the cell is required to operate.

Within the envelope there is disposed a resonant vane structure comprising two spaced apart thin metal plates 4 disposed in planes perpendicular to the axis of the envelope. Each plate 4 is secured centrally between adjacent portions of the rod 3 and comprises a first relatively wide capacitive portion 5 which extends radially from the rod 3 to a position closely adjacent the inner surface of the tube 1, and a second relatively narrow inductive portion 6 which extends from the rod 3 in a direction opposite to the capacitive portion 5 and at its outer end is electrically connected to the tube 1.

The dimensions of each plate 4 are chosen so that its capacitive and inductive portions 5 and 6 form a resonant circuit at the center of the range of frequencies over which the cell is required to operate. The plates 4 are at an electrical spacing from one another of a quarter wavelength at their resonant frequency and each plate 4 is spaced sufficiently far from the adjacent dielectric disc 2 for its resonant frequency to be substantially unaffected by the presence of the disc 2.

The cell also includes a keep alive electrode 7 of conventional form comprising an insulated conductor 8. The conductor 8 extends coaxially through a sealed side chamber 9 attached to the tube 1 and terminates close to a small aperture 10 formed in the wall of the tube 1 adjacent the outer end of the capacitive portion 5 of one of the plates 4, the insulation on the conductor 8 also terminating at this point so as to leave the end of the conductor 8 exposed.

The envelope contains a gas filling which is introduced via a pumping stem 11 which is subsequently sealed. The gas filling may typically consist of a mixture of helium and tritium in the atomic ratio 300 to l at a partial pressure of 0.7 torr and xenon at a partial pressure of 1.5 torr.

At each end the device is connected to coaxial connectors (not shown) of a form appropriate to the circuit in which the device is to be used.

In operation of the device radio frequency signals at power levels insufficient to ionize the gas filling will pass between the connectors with only small attenuation. With signals at power levels above a predetermined value voltage breakdown occurs at the gaps between the capacitive portions 5 of the plates 4 and the metal tube 1 causing the gas filling to ionize so that a short circuit is presented at the connectors- In sue in a T-R switch arrangement the cell is preferably disposed with the plate adjacent to the keep alive electrode nearer the receiver.

It will be appreciated that the dimensions of the vane structure in a device in accordance with the invention depend upon the frequencies at which the device is required to operate. Thus while in the arrangement described above, by way of example, the plates 4 are thin compared with their cross-sectional dimensions, this may not be the case in other arrangements in accordance with the invention.

In a similar arrangement to that described above intended for use as a T-B cell (not shown) the dielectric disc 2 nearer the keep alive electrode 7 is omitted and the envelope of the device is completed by a metal end wall, the metal end wall and the connector at the other end of the device being posi tioned so that at the frequencies at which the device is intended to operate, the device presents an open circuit at the connector when the gas filling is ionized, and a short circuit when the gas filling is not ionized.

I claim:

1. A gas-filled electric discharge device comprising: a sealed tubular envelope of conducting material and of substantially uniform cross section along its length; a gas filling within the envelope, a conductor which extends substantially coaxially through said envelope; a first member of electrically conductive material which is electrically connected to the conductor and extends radially from the conductor to a position closely adjacent the inner surface of the envelope so as to form a capacitive element; a second member of electrically conductive material which extends radially from the conductor all the way to the envelope and is electrically connected to both, so

as to form an inductive element; said capacitive and inductive elements forming a resonant circuit such that the application to the device of radio frequency energy at a frequency in a band containing the resonant frequency of the resonant circuit and above a predetermined power level causes ionization of the gas filling so that the device presents a short circuit to such energy, the device being effectively transparent to radio frequency energy at lower power levels.

2. A gas-filled electric discharge device according to claim 1 wherein said first and second members are formed integrally.

3. A device according to claim 1 wherein said first and second members extend in opposite directions from said conductor.

4. A device according to claim 1 wherein said conductor is in the form of a rod and each of said first and second members is in the form of a metal plate secured between adjacent portions of the rod.

5. A device according to claim 1 including a keep-alive electrode comprising a conductor terminating in the region of an aperture formed in said tubular envelope adjacent the outer end of said first member.

6. A device according to claim 1 including third and fourth members respectively corresponding to said first and second members so as to form a second resonant circuit at a frequency at which the device is intended to operate at an electrical spacing from said first-mentioned resonant circuit of substantially a quarter wavelength at said frequency.

7 A device according toclaim 1 wherein the riii'ii ii sists of a mixture of helium, tritium and xenon. 

1. A gas-filled electric discharge device comprising: a sealed tubular envelope of conducting material and of substantially uniform cross section along its length; a gas filling within the envelope, a conductor which extends substantially coaxially through said envelope; a first member of electrically conductive material which is electrically connected to the conductor and extends radially from the conductor to a position closely adjacent the inner surface of the envelope so as to form a capacitive element; a second member of electrically conductive material which extends radially from the conductor all the way to the envelope and is electrically connected to both, so as to form an inductive element; said capacitive and inductive elements forming a resonant circuit such that the application to the device of radio frequency energy at a frequency in a band containing the resonant frequency of the resonant circuit and above a predetermined power level causes ionization of the gas filling so that the device presents a short circuit to such energy, the device being eFfectively transparent to radio frequency energy at lower power levels.
 2. A gas-filled electric discharge device according to claim 1 wherein said first and second members are formed integrally.
 3. A device according to claim 1 wherein said first and second members extend in opposite directions from said conductor.
 4. A device according to claim 1 wherein said conductor is in the form of a rod and each of said first and second members is in the form of a metal plate secured between adjacent portions of the rod.
 5. A device according to claim 1 including a keep-alive electrode comprising a conductor terminating in the region of an aperture formed in said tubular envelope adjacent the outer end of said first member.
 6. A device according to claim 1 including third and fourth members respectively corresponding to said first and second members so as to form a second resonant circuit at a frequency at which the device is intended to operate at an electrical spacing from said first-mentioned resonant circuit of substantially a quarter wavelength at said frequency.
 7. A device according to claim 1 wherein the gas filling consists of a mixture of helium, tritium and xenon. 